The Collaborative International Dictionary of English v.0.48:

Erroneous \Er*ro"ne*ous\, a. [L. erroneus, fr. errare to err.
   See Err.]
   1. Wandering; straying; deviating from the right course; --
      hence, irregular; unnatural. [Obs.] "Erroneous
      circulation." --Arbuthnot.
      [1913 Webster]

            Stopped much of the erroneous light, which otherwise
            would have disturbed the vision.      --Sir I.
                                                  Newman.
      [1913 Webster]

   2. Misleading; misled; mistaking. [Obs.]
      [1913 Webster]

            An erroneous conscience commands us to do what we
            ought to omit.                        --Jer. Taylor.
      [1913 Webster]

   3. Containing error; not conformed to truth or justice;
      incorrect; false; mistaken; as, an erroneous doctrine;
      erroneous opinion, observation, deduction, view, etc. --
      Er*ro"ne*ous*ly, adv. -- Er*ro"ne*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

erroneous
    adj 1: containing or characterized by error; "erroneous
           conclusions"

Moby Thesaurus II by Grady Ward, 1.0:

137 Moby Thesaurus words for "erroneous":
   Albigensian, Arian, Catharist, Donatist, Ebionitist, Erastian,
   Gnostic, Jansenist, Jansenistic, Jovinianist, Jovinianistic,
   Lollard, Manichaean, Monophysite, Monophysitic, Montanist,
   Montanistic, Pelagian, Sabellian, Waldensian, Wyclifite, aberrant,
   abroad, adrift, adulterated, all abroad, all off, all wrong, amiss,
   antinomian, apocryphal, askew, astray, at fault, awry, barbarous,
   beside the mark, blemished, botched, bungled, careless,
   contrary to fact, corrupt, counterfeit, damaged, deceptive,
   defective, deficient, delusive, deviant, deviational, deviative,
   distorted, emanationist, errant, erring, fallacious, fallible,
   false, faultful, faulty, flawed, found wanting, heretical,
   heterodox, hylotheist, hylotheistic, illogical, illusory, immature,
   impaired, imperfect, imprecise, improper, impure, in error,
   inaccurate, inadequate, incomplete, incorrect, inexact,
   infelicitous, invalid, lacking, loose, makeshift, mediocre,
   misguided, misleading, mistaken, mixed, nonorthodox, not perfect,
   not right, not true, off, off the track, out, pantheist,
   pantheistic, partial, patchy, peccant, perverse, perverted,
   planetary, self-contradictory, short, sketchy, slipshod, slovenly,
   solecistic, specious, spurious, straying, truthless, unaccepted,
   unapproved, unauthentic, unauthoritative, uncanonical, undeveloped,
   uneven, unfactual, unfinished, unfounded, ungrammatic, unorthodox,
   unperfected, unproved, unscriptural, unsound, unthorough, untrue,
   wanting, wide, wrong